1. Field of the Invention
The present invention relates to a tire pressure monitoring system operable for detecting the installation of an unmonitored tire on a vehicle.
2. Background Art
A typical tire pressure monitoring system (TPMS) for a vehicle includes wheel units and a controller. Each wheel unit includes a transmitter, a pressure sensor, and a motion sensor such as an accelerometer. The wheel units are respectively installed to the tires of the vehicle and the controller is installed in the vehicle. Each wheel unit has a unique identifier to identify the tire to which the wheel unit is installed. The pressure sensors generate pressure signals indicative of the air (i.e., pneumatic) pressure of their associated tires and the motion sensors generate motion signals (e.g., bit-type information) indicative of whether their associated tires are moving or are stationary. A tire is rolling when the tire is installed on the vehicle and the vehicle is moving. A tire is stationary when the tire is installed on the vehicle and the vehicle is not moving or when the tire is stored in a vehicle compartment irrespective of vehicle movement. The transmitters transmit wheel unit signals containing the pressure and motion signals and the identifiers to the controller. The controller uses the identifiers to discern the pressure and motion signals for each tire. The controller determines the pressure of the tires based on the pressure signals and generates a warning for any tire having abnormal pressure.
The controller uses the motion signals indicative of whether the tires are rolling or are stationary in order to determine whether the tires are installed on the vehicle. For instance, if a tire is rolling, then the controller determines that the tire is installed on the vehicle. However, if a tire is stationary, then the controller uses knowledge of vehicle movement to determine if the tire is installed on the vehicle. To this end, the controller receives from the vehicle a speed signal indicative of vehicle speed (i.e., indicative of whether the vehicle is moving or is stationary). As such, if a tire is stationary and the vehicle is moving, then the controller determines that the tire is not installed on the vehicle. In this event, as the controller receives the motion signal for the tire indicating that the tire is stationary and as the controller is aware of the vehicle moving, the controller determines that the tire is stored in a vehicle compartment and another tire (such as a spare tire) is installed on the vehicle in place of the tire.
A vehicle having a TPMS typically includes four tires which are normally installed on the vehicle and a spare tire which is stored in a vehicle compartment for emergency use. The spare tire may be installed on the vehicle in place of a normally installed tire in the event that the normally installed tire is not functioning properly (e.g., when the normally installed tire is punctured and is flat). Each normally installed tire includes a wheel unit. The spare tire lacks a wheel unit.
The wheel units of the normally installed tires are registered with the controller such that the controller processes their wheel unit signals while ignoring other wheel unit signals (such as those transmitted by wheel units of nearby vehicles). That is, the wheel unit signals of the registered wheel units are valid wheel unit signals which are recognized and processed by the controller. These wheel units are considered “learned” wheel units by the controller by being registered with the controller. A normally installed tire is considered to be a “monitored” tire as a result of the controller being able to communicate with the wheel unit for the tire (e.g., being able to receive a valid wheel unit signal for the tire) when the wheel unit is functioning properly.
The controller does not receive a wheel unit signal for the spare tire as the spare tire lacks a wheel unit. As such, the spare tire is considered to be an “unmonitored” tire as a result of the controller not being able to communicate with the tire (e.g., not being able to receive a valid wheel unit signal for the spare tire). As a result, the spare tire is “incompatible” with the TPMS. Likewise, a normally installed tire is considered to be an unmonitored tire when its wheel unit is not capable of communicating with the controller. This may occur when the wheel unit is damaged or when the wheel unit is not registered with the controller (e.g., an “unlearned” wheel unit). That is, if the wheel unit of a tire is not able to communicate with the controller for any reason, then the tire is an unmonitored tire and is incompatible with the TPMS.
The TPMS is required to detect the installation of an unmonitored tire on the vehicle as certain regulations require that a warning be turned on to indicate the presence of an unmonitored tire on a vehicle. The TPMS can detect the installation of an unmonitored tire when the normally installed tires include motion sensors. For instance, if the vehicle is moving and a motion signal of a tire indicates that the tire is stationary, then the controller determines that the tire is not installed on the vehicle and that an unmonitored tire is installed on the vehicle in its place. Similarly, in the case of the vehicle moving and the controller receiving only three wheel unit signals (instead of four wheel unit signals during proper operation of the wheel units of the four normally installed tires), the controller determines that one of the tires installed on the vehicle is an unmonitored tire. The unmonitored tire may be a normally installed tire having a defective wheel unit, the spare tire, or a foreign tire having an unlearned wheel unit (i.e., another normally installed tire having an unlearned wheel unit).
Without the use of motion sensors, the requirement of detecting the installation of an unmonitored tire on a vehicle is a problem. For instance, in the event of a normally installed tire being stored in the vehicle compartment and the spare tire being installed on the vehicle in its place, the wheel unit of the normally installed tire continues to periodically transmit its wheel unit signal containing its pressure signal. (The transmitter of a wheel unit having a motion sensor typically transmits less often when the associated tire is stationary.) The normally installed tire is likely flat as a result of being replaced by the spare tire and its pressure signal indicates same. As a result, the controller is led to believe that the flat normally installed tire is on the vehicle and has an abnormal pressure. More importantly, the controller is not aware of the presence of the spare tire (i.e., an unmonitored tire) on the vehicle as the controller still receives four wheel unit signals (one wheel unit signal from the flat normally installed tire and three wheel unit signals from the remaining normally installed tires). As a result, the TPMS does not meet the requirement of detecting the installation of an unmonitored spare tire (i.e., a tire lacking a wheel unit) on a vehicle when a normally installed tire is stored in the vehicle compartment, the wheel units of the normally installed tires lack motion sensors, and the wheel units of the normally installed tires periodically transmit wheel unit signals.
Likewise, in the event of a normally installed tire being stored in the vehicle compartment and a foreign tire having an unlearned wheel unit being installed on the vehicle in its place, the controller is not aware of the presence of the foreign tire (i.e., an unmonitored tire) on the vehicle as the controller still receives the four wheel unit signals from the four normally installed tires which the controller considers valid along with a fifth wheel unit signal from the foreign tire which the controller considers non-valid and ignores. As a result, the TPMS does not meet the requirement of detecting the installation of an unmonitored foreign tire (i.e, a tire having an unlearned wheel unit) on a vehicle when a normally installed tire is stored in the vehicle compartment, the wheel units of the normally installed tires lack motion sensors, and the wheel units of the normally installed tires periodically transmit wheel unit signals.
It is desired to reduce the cost of the TPMS by eliminating motion sensors from the wheel units while meeting the requirement of the TPMS being able to detect the installation of an unmonitored tire on a vehicle.